HIV-1 clade C is currently responsible for more than 50% of new HIV infections and is now the most commonly transmitted subtype worldwide. While HIV-1-associated dementia (HAD) continues to be a major neuropathological manifestation of AIDS among clade B-infected individuals in the US and Europe, the incidence of HAD in regions like India and sub-Saharan Africa, where clade C infection is prevalent, appears to be lower. Whether the low apparent prevalence of neuroAIDS is due to underlying differences in HIV-clade pathogenesis or simply an artifact of confounding variables such as data sampling, clinical diagnosis or opportunistic infections is unclear. Potential differences in clade B and C neurovirulence and the mechanism by which HIV-1 infected brain mononuclear phagocytes (MP;perivascular macrophages and microglia) mediate pathogenesis have yet to be investigated. Our recent preliminary data indicates clade B viral strains may produce more neurotoxins, such as glutamate, during HIV-1 infection than clade C viral strains. We have shown previously that HIV-1 clade B infection of MP leads to enhanced glutamate production through the enzyme glutaminase. In this R21 application, we hypothesize that neurotoxicity is mediated through brain inflammation and the dysregulation of glutaminase in HIV-1-infected macrophages. In comparison to HIV clade B, we hypothesize clade C isolates will demonstrate decreased infection efficiency, altered cytokine/chemokine profiles, and decreased glutamate production by infected MP, providing mechanistic insight into differences between clade B and C infection of the brain. We will apply human monocyte-derived macrophage (MDM) infected by a panel of HIV-1 strains (HIV-1 laboratory clade B strains, primary clade B strains and primary clade C strains), to a severe combined immune deficient (SCID) HIV-1 encephalitis (HIVE) mouse model, thus modeling macrophage driven HAD in vivo. This approach will utilize laboratory assays that mimic HIV-1 infection and immune activation of brain MP to investigate the effects of the CNS immune response on production of inflammatory factors and neurotoxins as well as neuronal injury as it occurs during HAD. This application will establish a foundation of work detailing the differences between viral clades and the potential implications for HIV-induced brain inflammation and dementia. Determining the mechanisms by which HIV-1 infected MP and cytokines influence neuronal injury may identify new therapeutic strategies for treating HAD and other neurodegenerative disorders. HIV-1 viral strain clade C is currently responsible for more than 50% of new HIV infections and is now the most commonly transmitted subtype worldwide. While HIV-1-associated dementia continues to be a major neurological complication of AIDS among HIV-1 clade B-infected individuals in the US and Europe, the incidence of HIV-1-associated dementia in regions like India and sub-Saharan Africa, where clade C infection is prevalent, appears to be lower. This application will establish a foundation of work detailing the differences between viral clade B and C and the potential implications for HIV-induced dementia. It is our hope that determining the mechanisms by which HIV-1 influence neuronal injury may identify new therapeutic strategies for treating HIV-1-associated dementia and other neurodegenerative disorders.